Sharif Digital Repository

One of the challenges that always exists in the field of Testing the performance of converters, uninterruptible power supplies (UPSs) , etc. is to provide various types of loads to be applied to these equipments and test the quality of their performance in various load conditions. Leading or Lagging Power Factor loads, harmonic loads and non-linear loads are mainly required in this investigation. The use of inductors, resistors, capacitors and other devices for these tests is an old solution. Their disadvantages include high price, large volume and very high power loss, which was the initial idea of making programmable loads. A current source converter with the ability to Sink and source the... 

The goal of this thesis is the development and application of the finite volume method (FVM) with a same solution procedure in the fluid and structure domains for the simulation of fluid-structure interaction (FSI) problems in the compressible fluid flow. The unsteady Euler equations written in the arbitrary Lagrangian–Eulerian (ALE) form are considered as the governing equations of the compressible fluid flow and the moderate/large nonlinear deformation of the elastic structure is considered to be governed by the Cauchy equations in the Lagrangian/total Lagrangian forms. Therefore, the nonlinear phenomena in the unsteady compressible fluid flow and the large deformation of the elastic... 

In the present study, an incompressible smoothed particle hydrodynamics method based on vorticity-stream function (VSF-SPH) formulation is developed and assessed for simulating steady and unsteady incompressible flows. The vorticity-stream function formulation in the Eulerian reference frame is written in a Lagrangian reference frame to provide an appropriate incompressible SPH algorithm. The advantage of the proposed smoothed particle hydrodynamics method based on the vorticity-stream function (VSF-SPH) formulation over the weakly compressible SPH (WCSPH) is that the VSF-SPH method is a truly incompressible SPH algorithm and it does not involve any approximate enforcement of the... 

In the present study, the numerical simulation of incompressible laminar and turbulent flows using a high-order finite difference lattice Boltzmann method is presented. To handle curved geometries with non uniform grids, the incompressible form of lattice Boltzmann equation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting equation are discretized using the fifth-order WENO scheme. The advantage of using the WENO-LBM developed is that it needs less number of grid points and remains stable even at high Reynolds number flows. For the temporal term, the fourth-order explicit Rung-Kutta scheme is adopted for laminar flow calculations and... 

Nowadays, one of the most important desires of the human being is to reduce his living environmental pollution. Using the diluted combustion systems in new gas turbines in order to produce the minimum amount of has been done to satisfy this desire. It should be noted that reducing this amount and using the lower flame temperature will result in some consequences. The most important problem occurred in industrial and aerial gas turbines are the instability of the combustion due to dilution of the fuel to air mixture which it results in heat release fluctuations. If the heat release fluctuations and acoustic pressure are in the same phases, the amplitude of the fluctuations will increase which... 

In recent years, requirement to increase projectile performance, leads to a great interest in high angle of attack Aerodynamics. Projectile Maneuverability is a concept which is defined by having the capability to perform at high angles of attack while maintaining attached flow over the tail, rather than a capability of performing a mission in minimum possible duration. Interaction between body, wing and tail vortices can delay vortex breakdown over the wing and as a result may enhance projectile maneuverability. Studies show that wing aspect ratio and tail location have a remarkable influence on the vortices interaction and thus projectile maneuverability. In the present study, a series of... 

Throughout history, the occurrence of natural disasters and incidents has posed a potential threat to man-made constructions. Advancements in science and technology have led to the development of man-made civil infrastructures, which now exhibit increased complexity in terms of technological sophistication and spatial coverage. Consequently, monitoring and managing their health and risk factors have become more intricate. Urban lifelines, which encompass constructed utilities, transportation systems, telecommunication networks, and critical facilities, hold significant importance for the well-being of citizens. These infrastructure assets are essential for the distribution and flow of... 

Given the increasing importance of renewable energy and the environmental challenges posed by fossil fuels, this study primarily focuses on optimizing the use of solar energy and determining appropriate policies to increase investment in this sector. Residential buildings are among the major energy consumers, and given the available space on their rooftops, they provide a suitable location for the use of solar technology. Even when investors have the necessary financial resources, they prefer not to invest in this sector. This indicates an investment gap that government incentives could potentially bridge. However, previous government policies have failed to attract investors to this energy... 

The production of agricultural products is one of the most important human economic activities. The issue of mechanized and optimal use of pesticides is vital for human health and the environment, and the use of helicopters makes this possible. Although spray-based systems in helicopters are one of the most effective ways to produce agricultural products, it is still unclear how droplet movement in aerial spraying is affected by the complex downwash flow created by rotors. Modeling agricultural air spray to identify the spray trend of droplets in the air stream, downwash flows, and consequent vortices has attracted more attention as a result of the development of computational fluid... 

In the present work, the numerical solution of 2D inviscid compressible Magneto-hydrodynamic flow is performed by using the spectral difference (SD) method on quadrilateral grids. In this numerical method, similar to the discontinuous Galerkin (DG) and spectral volume (SV) methods, the concept of the discontinuous and high-order local representations is used to achieve conservation property and high-order accuracy. In the SD method, the test function or the surface integral is not involved and thus it has a simpler formulation than the DG and SV methods. In this numerical method, two sets of structured points, namely unknown points and flux points, are defined in each cell to support the... 

In this study, the viscous compressible flow is simulated over two-dimensional geometries by using the immersed boundary method and applying a high-order accurate numerical scheme. A fourth-order compact finite-difference scheme is used to accurately discretize the spatial derivative terms of the governing equations and the time integration is performed by the fourth-order Runge–Kutta scheme. To regularize the numerical solution and eliminate spurious modes due to unresolved scales, nonlinearities and inaccuracies in implementing boundary conditions, high-order low-pass compact filters are applied. A uniform Cartesian grid that is not coincident with the body surface is used and the boundary... 

In this study, two finite-difference lattice Boltzmann methods (FDLBM) are applied and assessed for the simulation of two-phase liquid-vapor flows with high density ratios. For this aim, the He-Shan-Doolen type lattice Boltzmann multiphase model is used and the spatial derivatives in the resulting system of equations are discretized by using the second-order central difference and modified Lax-Wendroff schemes. Suitable numerical dissipation terms and filters are applied to regularize the numerical solution and remove spurious waves generated by flow nonlinearities in smooth regions and at the same time to remove the numerical oscillations in the interface region of the two phases.Three... 

Considerable effort has been directed in recent years towards the transition metal complex catalyzed oxidation of organic compounds. Herein the synthsis of the iron complex of bis(oxazoline) ligand as a novel catalyst is reported, and the catalytic activity of this complex in oxidation of sulfides is investigated. Bis(2-oxazolynil)methane as ligand is prepared by condensation of diethylmalonate with 2-aminoethanole in 1:2 molar ratio and finally corresponding complex is synthesized by the reaction between FeCl3.6H2O and Bis(2-Oxazolynil)methane in 1:1 molar ratio. The complex is characterized by using IR, UV-Vis, cyclic voltametery, conductometery and elemental analysis data. Moreover,... 

In the present study, the preconditioned incompressible Navier‐Stokes equations with the artificial compressibility (AC) method formulated in the generalized curvilinear coordinates are numerically solved by using a high‐order compact finite‐difference scheme for accurately and efficiently computing the incompressible flows. A fourth‐order compact finite‐difference scheme is utilized to discretize the spatial derivative terms of the resulting system of equations and the time integration is carried out based on the dual time‐stepping method. The capability of the proposed solution methodology for computing the steady and unsteady incompressible viscous flows in a wide range of Reynolds... 

In this research, the numerical simulation of the natural convection is performed by using the smoothed particle hydrodynamics based on the artificial compressibility method. For this aim, the formulation of the artificial compressibility method in the Eulerian reference frame for the mass and momentum equations is written in the Lagragian reference frame and the Lagrangin form of the energy equation is also considered to compute the thermal effects. The benefit of the artificial compressibility-based incompressible SPH (ACISPH) method over the weakly compressible SPH (WCSPH) method for computing the natural convection is that there is no need in the formulation considered here to use any... 

In the present study, the numerical simulation of 2D inviscid compressible cavitation flow is performed by using the compact finite-difference method. The problem formulation is based on the multiphase compressible Euler equations with the assumption of the homogeneous equilibrium model and the system of baseline differential equations is comprised of the continuity, momentum and energy equations for the vapor-liquid mixture. To complete the system of governing equations, the ideal gas relation is used for the vapor phase and the Tait relation is applied for the liquid phase, and therefore, the compressibility effects are considered for both the vapor and liquid phases. To analyze the flow... 

In the present study, the shock-disturbances interaction in hypersonic inviscid flows considering real gas effects is numerically studied by using a high-order WENO scheme. To account for real gas effects, the equilibrium air model is utilized. The strong conservative form of the two-dimensional unsteady Euler equations in the generalized curvilinear coordinates is considered as the governing equations and a shock-capturing technique is applied. The resulting system of equations is discretized by using the fifth-order WENO finite-difference scheme in space and the explicit third-order TVD Runge-Kutta scheme in time to provide a high-order accurate flow solver. The WENO scheme is a stable scheme... 

On average there are to resistance spot welding connections per vehicle. The quality of these welding directly affects the quality of the finished product and the strength of the vehicle against various loads, including road roughness, different maneuvers and even sudden impacts from accidents. During the spot welding process, unintentional failures occur due to the wrong choice of current, force and time. The aim of this study is to investigate the fatigue strength of three-sheets welding joints in numerical and laboratory methods, considering the defects of (Undersize weld, Stick, edge of sheet metal and Edge of sheet metal-SECANT) . For this purpose, a healthy spot welding model was first... 

The numerical solution of the parabolized Navier-Stokes (PNS) equations for accurate computation of hypersonic axisymmetric flowfield with real gas effects is obtained by using the fourth-order compact finite-difference method. The PNS equations in the general curvilinear coordinates are solved by using the implicit finite-difference algorithm of Beam and Warming type with a high-order compact accuracy. A shock fitting procedure is utilized in the compact PNS scheme to obtain accurate solutions in the vicinity of the shock. To stabilize the numerical solution, numerical dissipation term and filters are used. The main advantage of the present formulation is that the basic flow variables... 

In this study, fluid-solid interaction (FSI) is simulated computationally by using a high-order accurate numerical method. The two-dimensional incompressible viscous flows are considered in the fluid domain. The primary problem with solutions of the incompressible Navier–Stokes equations is the difficulty of coupling changes in the velocity field with changes in the pressure field while satisfying the continuity equation. Herein, the artificial compressibility method is used to overcome this difficulty. Preconditioning is implemented to reduce the stiffness of the system of equations to increase the convergence rate of the solution. Using preconditioning, physical solutions even at low...